As a follow up on the Ice Machine Diagnosis post, I would like to bring your attention to a good article I read recently in the February 5, 2018 issue of the NEWS, a multimedia publication focusing on air conditioning, heating, and refrigeration. The article, Is Frost Accumulation Acceptable?, by John Tomczyk, provides tips for larger unit diagnosis’s. The article discusses the reasons for frost accumulation on a refrigeration system, usually seen at the compressor. Many technicians mistakenly add problems to a system by diagnosing frost at the compressor as liquid refrigerant at the compressor, then adjusting the TXV to raise the superheat. Tomczyk describes how to properly read superheat at the evaporator and the difference between this and total superheat, which is read at the compressor. He explains causes for frost build-up, and how to diagnose by checking superheat at the compressor. The article adds that the solution to low compressor superheat is in engineering controls, not adjustment of the TXV, which only controls the evaporator superheat.
I will add though, it is not only normal, but a good thing for the compressor to “sweat,” or moisture on suction lines and low side of the compressor , caused by dew point. Sweat means the system is working as designed, and more importantly, the refrigerant is cooling the compressor as designed. An abnormal build-up of frost, as Tomczyjk discusses, could mean low compressor superheat, which warrants a maintenance call.